1. Field of the Invention
The present invention relates to a multi-pair differential signal transmission cable formed by bundling together a plurality of differential signal transmission cables.
2. Description of the Related Art
Devices (e.g., servers, routers, and storage products) that deal with high-speed digital signals of several gigabits per second (Gbit/s) or more have adopted a differential interface standard, such as the low-voltage differential signaling (LVDS). Between devices or between circuit boards within a device, differential signals are transmitted through a differential signal transmission cable. Differential signals are characterized by having a high resistance to external noise while realizing a low-voltage system power supply.
A differential signal transmission cable includes a pair of signal line conductors, which are configured to transmit a plus-side signal and a minus-side signal having a phase difference of 180 degrees. A potential difference between these two signals is represented by a signal level. For example, if the potential difference is plus, a signal level “High” is recognized on a receiving side, and if the potential difference is minus, a signal level “Low” is recognized on the receiving side.
With a recent increase in transmission capacity, multi-pair differential signal transmission cables have come into use, which are each formed by bundling together a plurality of differential signal transmission cables. For example, Japanese Unexamined Patent Application Publication No. 2004-087189 (see, e.g., FIGS. 2 and 6) discloses a multi-pair differential signal transmission cable capable of transmitting many differential signals. In this document, a transmission cable (differential signal transmission cable) is disclosed, which includes a pair of insulated lines each formed by covering a signal line (signal line conductor) with an insulating layer (insulator), and a drain line. The transmission cable is obtained by covering the insulated lines and the drain line with a shielding material (shielding tape conductor), and covering the shielding material with a cushioning material. A transmission cable assembly (multi-pair differential signal transmission cable) is formed by bundling together a plurality of transmission cables with a shielding tape, a braided shield, and a jacket layer.